This invention relates generally to imaging and, more particularly, to generating images from projection data collected in a multislice imaging system. In at least one known imaging system generally referred to as a computed tomography (CT) system, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system and generally referred to as the "imaging plane". The x-ray beam passes through the object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is dependent upon the attenuation of the x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile.
In one known third generation CT system, the x-ray source and the detector array are rotated with a gantry within the imaging plane and around the object to be imaged so that the angle at which the x-ray beam intersects the object constantly changes. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal spot. X-ray detectors typically include a post patient collimator for collimating scattered x-ray beams received at the detector. A scintillator is located adjacent the post patient collimator, and photodiodes are positioned adjacent the scintillator.
Multislice CT systems are used to obtain data for an increased number of slices during a scan. One known multislice system includes detectors generally known as 3-D detectors. With such 3-D detectors, a plurality of detector elements form separate channels arranged in columns and rows. Each row of detectors forms a separate slice. For example, a two slice detector has two rows of detector elements, and a four slice detector has four rows of detector elements. During a multislice scan, multiple rows of detector cells are simultaneously impinged by an x-ray beam, and therefore data for several slices is obtained.
Images generated by a multi-slice scanner may, however, appear to be somewhat noisier than images produced by other known types of scanners, such as CT/i scanners, at the recommended x-ray tube current reduction factor. At least one known embodiment of a multislice scanner uses a shorter geometry which increases image noise away from the center of the image compared to other known longer geometry scanners. More particularly, and as a result of the geometry change and the fan beam reconstruction in the multislice system, to reduce the concentric force on the x-ray tube, the x-ray tube to iso-center distance needs to be reduced. Consequently, the magnification factor for such scanner increases, the scaling factor used in the fan beam backprojection increases, and the noise in the reconstructed image also increases. It would be desirable to provide that an image generated from data collected in a short geometry multislice scan has about the same image quality, e.g., noise reduction, as images generated by other types of scanners.